This invention relates to stabilized polyvinyl chloride compositions and more particularly to stabilizer compositions comprising a phosphite compound, an organo zinc compound and a sulfur-containing organo tin compound and to polyvinyl chloride compositions containing such stabilizers.
The use of organo tin mercapto carboxylic esters or organo tin mercaptides as stabilizers for polyvinyl chloride (PVC) has long been known and such compounds have gained wide acceptance in the PVC compounding art. Because of their low toxicity and stability at elevated processing temperatures, as well as the excellent initial color and clarity of the resulting PVC compositions, these compounds are particularly desirable in preparing rigid and semi-rigid PVC compositions for use in food packaging applications. In as much as alkyl tin compounds are quite expensive, the art has continued to seek alternative, lower-cost stabilizer and co-stabilizer systems, and to identify synergists and boosters for use with alkyl tin mercaptide stabilizers that would permit reducing the use level of the tin compound and thus lower the overall costs. Among the co-stabilizers identified for such use are those disclosed in U.S. Pat. Nos. 3,925,246, 3,632,538 and 3,953,385. Such co-stabilizers have included additional tin sulfide compounds, complex tin esters, hindered phenols, phosphites, epoxy compounds and metal soaps. Particular combinations of hindered phenols and phosphites have also been disclosed in U.S. Pat. No. 3,998,782 to be useful stabilizers for PVC, and these may be further combined with epoxy compounds, tin compounds, metallic soaps and the like.
Although these and similar stabilizing systems have had some success, the generally held view in the art is that none possess the attractive combination of high temperature stability, good initial color and long term stability characteristics typical of organo tin mercaptide compounds. A stabilizer system having such characteristics while reducing the requirement for the very expensive organo tin mercaptides would thus be a useful advance in the PVC compounding art.